In sport mode, even under slow acceleration, I have what I can only describe as a mechanical open/shut noise. When car moves from S3 to S4  Sounds worse if accelerating hard. If in dive or economy mode, say in D7 and put accelerator into floor it drops to D4 and I get a similar noise. I don’t notice noise in drive or economy when car progressing through the gears. No warnings on dash. Been on diagnostics today and no error messages. Given it’s not happening for all gear changes I can’t see it being the clutch, drive at moment appears unaffected. Any thoughts?  Is this an expensive bill pending? Thanks

Stop driving untill you find the fault. Check auto oil level and /or change the oil in the gearbox. If not sure how to do it, take it to a autobox specialist. You should find one in your area if you google?